1. Field of the Invention
This invention relates to autonomously maintaining a synchronous system image in a parallel systems complex (parallel sysplex). More particularly, the invention relates to autonomously updating and maintaining a consistent system image across a number of systems as they come online and offline.
2. Description of the Related Art
As businesses grow and develop, so do their data processing and transaction management needs. Updating and upgrading computer equipment that manages these transactions is often costly and may require significant downtime which causes further disruption and expense. In response to these problems, computing service providers currently offer the ability to group systems into a sharing systems complex; for example, IBM's Parallel Sysplex environment. These services allow an entity to connect a group of computers which will share resources and balance workloads, increasing the capability of the systems operating individually, while allowing new computers or hardware to be added to the Parallel Sysplex without taking the entire Sysplex system down. Thus, an entity can easily upscale computing capability using previous equipment and simultaneously maintain continuous application availability.
A user may further implement an IMSplex in a Parallel Sysplex environment. The IMSplex consists of one or more IBM Information Management Systems (IMS) that work together as a unit while offering the user the ability to manage multiple IMS systems as if they were a single system. This single system image allows the user to more easily manage multiple systems. The IMS database management system itself is composed of application programs, transactions, and databases. IMS requests act on transactions, databases, and area resources. In an IMSplex, transactions are placed in a shared queue, and IMS members of the IMSplex with available capacity pull work from the queue and process it.
In order to maintain this single system image and allow the IMSplex to operate properly, the IMS members in the Sysplex must have a synchronous view of the status of the IMS resources. If the IMS members that make up the Sysplex do not have the same resource status information, then errors may be introduced. For example, a user may issue a request directing that a particular transaction be stopped. If one IMS does not receive the request or otherwise does not know that the transaction should be stopped, it may begin work on the transaction which was not intended to be executed. If the transaction was stopped in order to allow changes to be made to it, the work queued by the IMS that was processing the transaction may have had the wrong attributes, in which case it will generate bad results.
The problem of maintaining a single system image manifests itself when an IMS is added to the Sysplex and when an IMS member of the Sysplex is taken offline or crashes, and is subsequently booted back up. These IMS members will not have the current picture (image or state) of the resource status that the online IMS members do; the new IMS or rebooting IMS cannot be allowed to process work until the IMS coming online shares the same image as that held by the other IMS members of the Sysplex.
Typically, a user would have to keep track of the status and issue requests on the Sysplex and at the newly started IMS or restarted IMS in order to bring the IMS coming online in synch with the Sysplex members. The process is cumbersome and requires time, effort, and skill on the part of the user; in addition, user error (such as missing or forgetting a particular request) may later generate errors that must be located and reversed.
Other solutions include polling between IMS members for changes and determining based on the poll results a proper or expected Sysplex status. However, polling and monitoring the behavior of the IMS members adds additional work to the system and is cumbersome to implement. If no changes have occurred, processing overhead in conducting the polling is wasted.